The present invention relates to a dynamic friction coefficient measuring apparatus capable of continuously measuring and automatically recording dynamic friction forces between two different objects according to speeds.
For example, for measuring a dynamic friction force between a road surface and an automobile tire, there has heretofore been used a pendulum type measuring apparatus. However, this pendulum type measuring apparatus has been applicable to the measurement of friction only when the speed relative to the road surface is within a fairly low speed range. But, the friction coefficient of the road surface differs considerably according to running speeds of an automobile. Generally, the higher the speed, the smaller the friction coefficient. Besides, it is at a high speed of 40 km/H or more that such friction coefficient becomes a subject of question. Therefore, in order to measure the friction coefficient correctly, it is necessary that the speed be measured under the same condition as the actual speed and that the pressure be also measured under the same condition as the actual pressure of ground contact of a tire.
To satisfy such requirements, the present inventor has already proposed a friction coefficient measuring apparatus (see Japanese Patent Publication No. 57-23212) including a friction measuring portion, the friction measuring portion comprising a disc-like body with a road surface friction measuring rubber member attached thereto, a disc as a rotating body capable of rotating about the axis of the disc-like body, the disc-like body and the disc being interconnected through a first spring member, and a pen holder capable of moving in the radial direction of the disc, the pen holder being connected to the disc through a second spring member, in which the relation between the speed of the friction coefficient measuring rubber member and the amount of displacement in the radial direction of the pen holder during rotation of the friction measuring portion, and the relation between the angle of torsion of the disc relative to the disc-like body and the friction coefficient, are calibrated in advance to thereby record the relation between the friction coefficient and the speed automatically.
However, such friction coefficient measuring apparatus has encountered a limit in measurement accuracy due to a sliding friction in the radial direction of the pen holder and that between the pen and the recording paper. Besides, the pen holder moves during a preliminary rotation of the disc-like body and the disc, thus allowing unnecessary recording to be made and making it difficult to read data. Further, the operation for attaching and detaching the pen and that for fixing the recording paper are troublesome, and thus the working efficiency is poor.
Accordingly, it is the object of the present invention to provide a dynamic friction coefficient measuring apparatus capable of automatically recording the relation between speed and friction coefficient, attaining a high measurement accuracy and easily reading data and being easy to handle.
It is another object of the present invention to provide a dynamic friction coefficient measuring apparatus which, once set on a road surface, permits a continuous and automatic recording of the relation between speed and friction coefficient, attains a high measurement accuracy and an easy reading of data, and is easy to handle.